Transport of carnitine in neuroblastoma NB-2a cells.

Carnitine accumulation was measured in cultured neuroblastoma NB-2a cells. This process was found partially sodium dependent and its kinetics to be a sum of a saturable transport (Km = 123 +/- 13 microM) and diffusion (D = 63 +/- 7 pmol/mg protein/min/mM). On the contrary to previous reports on neural cells, the accumulation of carnitine was found insensitive to gamma-aminobutyric acid (GABA). Measurements of carnitine accumulation in the presence of different compounds resulted in the conclusion that carnitine transport does not occur through the known systems specific toward choline and/or amino acids. For instance, an observed inhibition of carnitine transport by serine and cysteine, without any effect of alanine, excluded a possible role of ASC amino acid transport system. An involvement of a new transporter is thus postulated, specific toward compounds with a polar group in the beta position with respect to the carboxylic group.